1. Field of the Art
This invention relates to an IC device contactor to be used with an IC test machine for electrically connecting thereto spherical electrodes of IC devices, for example, of CSP (chip scale package) type or of BDA (ball grid) type for a test of electrical properties or characteristics.
2. Prior Art
IC devices consist of an LSI (large scale circuit) chip with a predetermined number of electrodes. LSI chip are provided as packages shielded in a synthetic resin material. Connected to a large number of electrodes on an LSI chip are lead pins which are generally led out on one side of a package. Lately, however, to comply with demands for IC devices of smaller sizes, there have been developed and put in use IC packages which are reduced almost to the size of an LSI chip and provided with a large number of electrodes substantially of hemispherical shape like solder balls or electrodes of spherical shape arranged in a matrix on a surface on one side of a package instead of lead pins. The packages of this sort are called CSP or BGA and, since they require only a small mounting space on a printed circuit board, have found wide applications in mobile type electronic appliances, for example, such as handy video cameras, mobile or cellular phones, notebook type personal computers etc, contributing to downsizing these electronic appliances to more compact forms.
In testing or measuring electrical properties of the afore-mentioned CSP and BGA type IC devices in a post-production stage, each IC device package is connected to an IC tester by the use of contact probes which are electrically connected to the respective spherical electrodes of IC devices. For this purpose, usually mounted on the IC tester is a socket board which has the same number of contact elements as the spherical electrodes on the part of IC devices to serve as part of a contacting mechanism for IC devices under test. During a test, IC device are pressed against the socket board, thereby to electrically connect the contact elements on the side of the IC tester to the spherical electrodes on the side of the IC device.
In this connection, the electrode on an IC device is formed in a fine pitch matrix within a small surface area of square shape. For example, more than 150 minute electrodes are arranged in a matrix within a small surface area of several cm.sup.2. Besides, since the electrodes of IC devices are spherical in shape, difficulties are often encountered in maintaining stable electrical connections with the contact elements on the side of the socket board for all of the electrodes. Especially in case the spherical electrodes on an IC device is formed by solder balls, their surfaces tend to be oxidized and covered with an oxidation film which would increase the possibilities of contact failures all the more.
Therefore, instead of bringing electrodes on the part of a socket board directly into contact with electrodes of IC devices, it has been the general practice to interpose an anisotropic conductive sheet between a socket board and each IC device to be tested. The anisotropic conductive sheet is constituted by a sheet of resilient material and of a predetermined thickness, for example, by an insulating sheet of silicon rubber and fine conductive wires of a metal such as fine gold-plated brass wires which are embedded in the silicon rubber sheet. The fine conductive wires are extended from one side to the other of the insulating sheet in an angularly oriented state, and the opposite ends of the wires are exposed in the surfaces on the opposite side of the insulating sheet. As the anisotropic conductive sheet is interposed and pressed against the socket board, the embedded fine conductive wires are electrically connected to the contact elements on the socket board. In this regard, in order to maintain electrical connections between the contact elements and fine conductive wires in a securer manner, each electrode should desirably be contacted by a plural number of fine conductive wires of the anisotropic conductive sheet. Accordingly, when IC devices are set in contacting positions, the spherical electrodes are located in offset positions relative to the contact elements on the side of the socket board, and, according to the degree of angular orientation, fine conductive wires in the anisotropic conductive sheet can provide an increased contacting length to ensure securer electrical connections between the IC device and the socket board.
In an IC device test, it is the anisotropic conductive sheet that is directly contacted by the spherical electrodes of IC devices. Namely, it is the anisotropic conductive sheet that receives impacts repeatedly by connections of IC devices. In addition, in order to test electrical properties of IC devices efficiently, it has been the general practice to test a plural number of IC devices simultaneously, for example, to set as large as 16, 32 or 64 IC devices on a test board and to press the test board against a socket board. Therefore, an extremely large number of electrodes have to be connected at once, by applying a strong compressive force to ensure that all of the electrodes are connected without failures. Due to repeated contact with IC device electrodes under compressive force, the anisotropic conductive sheet of this sort always has a problem of getting worn out or deteriorated prematurely.
Further, the spherical electrodes on IC devices are of a soft metal like solder balls which can be scraped off quite easily when pressed against an anisotropic conductive sheet for contact therewith and may deposit on the latter as solder debris. Contact failures may result from such solder debris short circuiting the fine conductive wires. Especially, since fine conductive wires are provided in a high density on the entire surfaces of the anisotropic conductive sheet, short circuiting across adjacently located solder balls is very likely to occur upon connecting IC devices to an anisotropic conductive sheet on which a large amount of solder debris has deposited. Further, when mounting an IC device of this sort on a wiring board, its spherical electrodes are connected to electrodes on the side of the wiring board after being softened or fused by application of heat. From the standpoint of ensuring stability of electrical connections of the electrodes of IC device mounted on a wiring board, the apex portions of the spherical electrodes should preferably be maintained perfectly in a spherical shape. Nevertheless, there has been a problem that the apex portions of the spherical electrodes can be damaged to a material degree if abutted directly against fine conductive wires of an anisotropic conductive sheet.